Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Add API(v2) to add environment to task"
  - Add API(v2) to add environment to task

    JIRA: YARDSTICK-736

    API: /api/v2/yardstick/tasks/<task_id>
    METHOD: PUT
    PARAMS:
    {
        'action': 'add_environment',
        'args': {
            'environment_id': environment_id
        }
    }

    Change-Id: Idc31cb21de882d008202b6395158e9f9aa9244db
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index ac1f30a..edec11f 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit ac1f30a97b9c26762d66f2914928f1cb7e9a7697
+Subproject commit edec11f71207d6df007460cd19ccab08201d60c6